The present invention relates to a technology which is effectively applied to a high frequency power amplifier circuit and a high frequency power amplifier electronic component incorporating the high frequency power amplifier circuit. More specifically, the present invention relates to a technology for reducing variation in bias point in a high frequency power amplifier circuit which applies bias to an amplifier transistor in current mirror configuration, and a manufacturing method for the high frequency power amplifier electronic component.
The transmission-side output unit of radio communication equipment (mobile communication equipment), such as cellular phone, incorporates a high frequency power amplifier circuit. The high frequency power amplifier circuit uses a semiconductor amplifier element, such as MOSFET (field-effect transistor) and GaAs-MESFET. (In general, the high frequency power amplifier circuit is formed in multistage configuration.)
The high frequency power amplifier circuit is often constituted as one electronic component which is formed as follows: a semiconductor chip including an amplifier transistor and a bias circuit for it, a supply voltage control circuit, and the like is mounted over an insulating substrate; the insulating substrate comprises, for example, a ceramic substrate, and has printed wiring formed over and in it; and the semiconductor chip is mounted together with other semiconductor chips and discrete components, such as capacitors, and these components are connected by the above printed wiring or bonding wires. This electronic component is designated as RF power module.
With respect to the semiconductor chip for use in RF power modules for cellular phone, the packing density has been being increased for enhancement of the performance of and reduction of the size of modules. Recently, inventions related to such RF power modules as illustrated in FIG. 14 have been proposed from the viewpoints of stabilization of high frequency power amplifier characteristics. (Refer to patent Document 1, for example.) The RF power module illustrated in FIG. 14 is provided with a bias transistor Q1 whose gate is connected with that of an amplifier transistor Q2. The RF power module operates as follows: a bias current Ib is generated by a current mirror circuit which comprises transistors Q3 and Q4 and duplicates a current from a constant current source CI. This bias current Ib is passed through the bias transistor Q1, and the amplifier transistor Q2 is supplied with bias in current mirror configuration.
In such an RF power module that applies bias to an amplifier FET in current mirror configuration, the drain current passed through the amplifier transistor Q2 does not change even if the threshold voltage (Vth) of the FET varies. Therefore, advantages of unnecessary correction and enhanced yield are brought.
[Patent Document 1]
Japanese Unexamined Patent Publication No. 2003-017954